Effect Of Additives On The Aggregation Behavior Of Carboxylate Gemini Surfactants With A Long Rigid Spacer

The spacer is the key structural factors responsive to the rich aggregation of Gemini surfactants. During the past decades, less attention has been paid to the Gemini surfactants with long rigid spacer. However, the distinctive self-assembly of this type of surfactants have been revealed in a few studies, such as the "aging effect" at air/water interface, strong ability in constructing threadlike micelles. Besides, one special network-like aggregates formed by C12φ2C12 at low concentrations have been discovered in our group, In this dissertation, we further explore the effect of additives on the aggregation of Cmφ2Cm(m=10、12), the main contents are summarized as follows:1)The effect of salts on the network-like aggregates formed by C12φ2C12 has been studied mainly using dynamic light scattering measurements. The results show that the network-like aggregates are sensitive to the salts. A fast transition from the network-like aggregates to the core-shell micelles is induced by small addition of salts. This is caused by the association between the counterions and the ionic head groups of C12φ2C12 through electrostatic interactions, the fragile hydrophile-lipophile balance in the network-like aggregates formed by C12φ2C12 can be destroyed. The counterions of the salts with higher charge density show higher efficiency in inducing the aggregate transition. The transiton efficiency for Bu4NBr is even higher than NaCl, this is attributed to the additional hydrophobic interaction between the butyls of Bu4NBr and alkyl tail of　C12φ2C12.2) The effects of alkyltrimethylammonium bromides, CnNBr, on the network-like aggregates formed by Cmφ2Cm (m=10、12) has been studied using dynamic light scattering and rheological techniques. Compared with the salts, smaller amount of CnNBr can induce the transiton of network-like aggregates into thread-like micelles and promote a fast micelle growth. With increasing the CnNBr concentration, the molecular geometry of Cmφ2Cm is further modified, the threadlike micelles transform into vesicles. The effective packing parameter Peff has been estimated, which is consistent with experimental results very well. These results benefit from both the columnar-like molecule geometry of Cmφ2Cm and the geometry modification by the interaction with CnNBr.3)The temperature induced vesicle aggregation of Cmφ2Cm(m=10、 12)/CnNBr vesicle has been studied using tubidity and dynamic light scattering. The results show that the vesicle critical aggregation temperature(Tc) will be decreased if the alkyl tails of Cmφ2Cm and CnNBr become short. However, Tc cannot be effectively lowered by changing the molar ratio of two components or addition of NaBr. The possible reason of vesicle aggregation is the hydrophobic interaction between Cmφ2Cm tails. When the temperature reaches Tc, one of Cmφ2Cm tails stretches out of the molecular layer of the vesicle and interact with other tails from other vesicles by hydrophobic interaction. The vesicles should been thus drawn close and aggregated.